Cutting tool

ABSTRACT

A cutting tool, especially a drill, milling cutter, screw tap, reamer and core drill, comprising a shaft and a cutting member on which at least one cutting edge is provided for machining a workpiece, the cutting member being provided with a slide layer which has a lower hardness than a base layer of the cutting member.

The invention relates to a cutting tool such as a drill, milling cutter,screw tap, reamer or core drill in accordance with the preamble of claim1.

The use of numerically controlled machine tools has been a substantialcontribution to increasing the productivity, flexibility, manufacturingquality and efficiency of modern production apparatuses. The versatilepossibilities of control technique and information processing have beenresponsible for machine designs suited for use in automaticmanufacturing systems. Systems of this kind are usually equipped withtool and workpiece storage means, automatic changing means andintegrated measuring stations so that the steps to be manually taken bythe machine operator are minimized. Sensors for monitoring machinefunctions and process states, such as wear and breakage of tools, ensurethe automatic manufacturing sequence. In order to be able to exploit thefull capacity of such machine tools, in parallel with the development ofmachine tools also appropriate tools have to be provided which permit aprolonged tool life as well as an increase in the cutting speeds so thatthe manufacturing times can be reduced to a minimum. However, in thecase of modern machining processes the increase in the cutting speedneed not necessarily be of major importance, but with particularapplications, such as the machining of light metals, for instance, itmay be endeavored to dispense with coolants and lubricants or at leastto reduce the use thereof and, on the other hand, to accept a reducedcutting speed.

In the case of tools having geometrically defined cutting edges, suchas, e.g., drills, milling cutters, reamers, screw taps, core drillsetc., preferably high-alloy tool steels, hard metals, i.e. sinteredmaterials of metallic hard materials such as, for instance, cermet,ceramic insert, monocrystalline diamond, polycrystalline diamond,polycrystalline boron nitride etc. are employed as cutting materials.

Moreover, there are known tools in which the wear resistance of thetools is further increased by coating them with hard material layers,such as, e.g., titanium nitride, titanium carbide and aluminium oxide.

In DE-OS 23 57 134 a cutting tool is disclosed in which a coating filmof precious metal is applied by an ion-plating method. DE-AS 12 71 495relates to a method of manufacturing a cutting tool in which a coverlayer of copper or brass is applied to the portions not to be hardenedprior to a hardening operation.

The cutting tools known from the two a.m. publications have the commondrawback that, on the one hand, the cover layers consist ofcomparatively expensive materials and the tool lives are improvable,especially when light metals are processed.

The continuous development of the machine tools and the use of novelmethods, such as dry machining, for instance, where the workpieces aremachined without using coolants/lubricants or machining with reducedamounts of coolant, and the endeavor to obtain more and more reducedmanufacturing tires make requirements to the tools as regards the toollives and the maximum obtainable cutting speeds which cannot be fullymet by conventional tools.

The object underlying the invention is to provide a cutting tool whichhas a simple design and permits an improved tool life while, at the sametime, the cutting speed is increased or the amount of coolant isreduced.

This object is achieved by the features of claim 1.

The tool wear can be considerably reduced by the measure to apply a softslide layer containing sulphides, selenides, tellurides, such as, e.g.,MoS₂, NbS₂, TaS₂, WS₂, MoSe₂, NbSe₂, TaSe₂, WSe₂, MoTe₂, NbTe₂, WTe₂ ormixed compounds, to the cutting tool, because the chip slides off thesoft slide layer and thus the face wear is reduced and the formation ofa built-up edge is prevented. Moreover, the friction between the tooland the open face is minimized so that the wear of the open face isreduced, too. Thus the tool life can be considerably improved by theslide layer according to the invention compared to conventionalsolutions. There are already known some coating methods for applyingwearing coats to cutting tools so that a respective description isdispensed with. A method of the co-applicant VILAB AG/Switzerland hasturned out to be especially suited.

It is of particular advantage to apply the soft slide layer to awear-resisting base layer which, in turn, has been applied to the basebody of the cutting tool so that the latter is provided with two layers.

In order to ensure an optimum machining operation, the soft slide layeris not applied in the area of the cutting edge.

It is especially advantageous when the base body of the cutting tool ismade of HSS, hard metal, cermet or ceramic material and thewear-resisting layer consists of TiN, TiAlN, TiCN, diamond or the like.

Depending on the application, it is preferred to apply the base layer ina thickness of 1-10 μ, while the hardness of the base layer should bebetween 2000-10000 UV and the slide layer should have a Mohs' hardnessof 1-2.

The measure to form one or a plurality of grooves, especially in groovedshape, in the flute promotes breakage of chips so that the formation oflong flowing chips, which interfere with the operating cycle, e.g. inautomatic machine tools, and impede the chip removal, is prevented. Withthe short discontinuous chips a high surface quality is guaranteed,while the chips can easily be removed. Moreover, in the case of wetmachining the groove facilitates the supply of coolants and lubricantsto the cutting portion of the tool so that the stability thereof isincreased and the carrying-off of the chip is further facilitated.

Preferably a plurality of grooves extending along the flute at paralleldistance is formed in the face.

The chip formation and the chip discharge can be further improved byproviding also the open space with groove-like recesses extending awayfrom the cutting edge. The supply of coolant and lubricant, too, can befurther improved by such recesses compared to the above-describedembodiment.

The chip capacity and the tool times of such a tool are superior tothose of conventional tools, even if the workpieces are machined in adry state or with reduced supply of coolant.

In case that the cutting edge is formed at the front of the cuttingmember, such as, e.g., in drills, face mills, core drills etc., therecesses are advantageously formed as segments of a circle or spiral onthe open face which are positioned approximately concentrically withrespect to the axis of the cutting tool.

The chip formation and the supply of coolant and lubricant can befurther improved by the fact that a recess is associated with eachgroove so that the recess is practically arranged in extension of agroove.

In special cases of application it may be advantageous to form thegrooves or recesses only over a partial area of the flute and the openspace, respectively.

It has proved especially advantageous when the width and the depth ofthe grooves and/or the recesses is between 0.02-2 mm, preferably0.02-0.5 mm.

Further advantageous developments of the invention are described in thesubclaims.

In the following, preferred embodiments of the invention are explainedin detail by way of schematic drawings.

FIG. 1 is a view of the cutting member of a twist drill;

FIG. 2 is a diagrammatic top view on a bit of a drilling tool;

FIG. 3 is a three-dimensional sectional view of a cutting tool accordingto the invention;

FIG. 4 is a schematic diagram for explaining the chip formation in acutting tool according to the invention;

FIG. 5 is a diagram comparing a conventional cutting tool with a cuttingtool according to the invention, and

FIG. 6 is a diagram comparing a conventional cutting tool with a cuttingtool provided with a slide layer.

FIG. 1 shows the cutting member 2 of a twist drill 1 which has twospiral flutes 4, 5 extending along the cutting member 2 to the bit 6 ofthe drill. Each major cutting edge 8, 9 is formed at a wedge which, onthe one hand, is formed by an open face 10 and, on the other hand, by aface 12 of the flute 5.

Moreover, in the shown embodiment groove-like recesses 14 extendingconcentrically from the major cutting edge 8 (9) to the rear edge 16 ofthe open face are formed in the open face 10.

In each flute 4, 5 a plurality of adjacent grooves 18 is formed the axisof which is disposed approximately in parallel to the axis of the flute5 (4), i.e. the grooves 18 extend likewise spirally about the axis 20 ofthe drill 1. As regards further details about the design of the grooves18 and the recesses 14, reference is made to FIGS. 2 and 5.

As is further indicated in FIG. 1 by dot-dash lines, the drill 1 andespecially the cutting member 2 are coated with a slide layer 20 whichis not applied, however, in the area of the major cutting edges 8, 9.The slide layer 20 preferably comprises sulphides, solenides,tellurides, such as, e.g., MoS₂, NbS₂, TaS₂, WS₂, MoSe₂, NbSe₂, TaSe₂,WSe₂, MoTe₂, NbTe₂, WTe₂ or mixed compounds thereof. When applying suchslide layer 20 the areas of the bit 6 indicated by dot-dash lines werecovered by an adequate material so that the major cutting edges 8, 9 areconstituted by a harder material. Regarding further details about theslide layer 20, the following FIGS. 3 and 6 are referred to.

FIG. 2 shows a schematic top view on the bit 6 of the drill 1, whereinmerely the faces of the drill bit 6 are represented, whereas the minorcutting edges of the drill rotating outside the plane of projection havebeen omitted.

As one can take from this view, the two open faces 10, which areconfined in the view according to FIG. 2 an the one hand by the majorcutting edges 8 and 9 and, on the other hand, by the rear edges 16, areformed by the two flutes 4, 5. The radially outer confinement of theopen faces 10 is effected by the minor cutting edges 22 and the minoropen faces 24. The two major cutting edges 8, 9 are connected by thechisel edge 26 extending through the axis 27 of the drill, On each openface 10 the recesses 14 are incorporated, as mentioned already before,which are formed in the illustrated embodiment as segments of a circleor spiral concentrical with respect to the axis 27 of the drill 1. Eachof the circular lines shown in FIG. 2 represents the bottom of a recess14. According to FIG. 2, moreover the grooves 18 extending approximatelyperpendicularly to the plane of projection along the flutes 4, 5 areformed in the faces of the flutes 4, 5 (perpendicular to the plane ofprojection). Both the grooves 18 and the recesses 14 have anapproximately undulated or U-shaped cross-section so that the majorcutting edges 8, 9 are formed in wave shape. The depth and width of thegrooves 18 and/or the recesses 14 is approx. between 0.01-2 mm,preferably 0.02-0.5 mm, depending on the individual case.

The slide layer 20 mentioned at the beginning is not formed in the areaof the major cutting edges 8, 9 so that only the areas between thedot-dash fine in FIG. 2 and the rear edges 16 of the open faces 10 arecovered with the slide layer 20.

In special cases of application it may also be of advantage to extendthe slide layer 20 to the cutting edges 8, 9.

Due to the wave shape of the faces 12 of the flutes 4, 5 and the openfaces 10, the supply of coolant/lubricant—if used—to the major cuttingedges 8, 9 is considerably improved so that the wear of the drill 1 canbe substantially reduced or else the amount of coolant can be reduced.Moreover, the undulated structure of the flute entails an earlier chipbreakage so that—as already mentioned in the beginning—comparativelyshort discontinuous chips are formed which ensure a high surface qualityand, at the same time, can easily be discharged.

The superiority of this “grooved section”, as it is called, vis-a-visthe conventional ground sections is emphasized in FIG. 5. This is acomparison of the tool life travel of two twist drills, one of which wasprovided with a plane open face and a planar face or flute, while thecomparison tool was provided with the grooved section according to theinvention at the flutes 4, 5 and the open faces 10. A workpiece of42CrMo4V was machined by both drills, wherein the two drills were notprovided with the above-mentioned slide layer 20, Both twist drills hadidentical geometrical dimensions—apart from the grooved section —andwere operated at the same cutting speed v_(c), the same feed f and thesame cutting depth a_(p).

As one can take from FIG. 5, solely by providing the grooved section thetool life travel can be substantially improved compared to conventionaltools so that the tool lives and the maximum obtainable cutting speedsof the tools according to the invention are superior to those ofconventional tools especially in the case of dry machining or in thecase of machining with a reduced amount of coolant/lubricant.

FIG. 3 represents a three-dimensional view of a drilling tool, wherein,for the sake of clarity, the grooves 18 in the flutes 4, 5 are indicatedas dashed lines in the area of the major cutting edges 8, 9. Therecesses 14 in the open faces 10 are indicated merely as dot-dash lines,because by way of FIG. 3 the coating of the drill 1 is to beillustrated.

The base body of the drill may be manufactured of conventional HSSsteel, for instance, wherein either the entire drill or, as indicated inFIG. 3, merely the cutting member 2 is provided with a hard base layer26. This base layer 26 may consist, e.g., of a hard ceramic materialsuch as TiN, TiAlN, TiCN or of diamond etc. As mentioned already at thebeginning, the PVD coating method is not discussed here, to simplifymatters, but reference is made to the relevant literature and, inparticular, to the respective patent application of VILAB.

The base layer 26 extends to the major cutting edges 8, 9, wherein inFIG. 3 the hatching indicative of the base layer 26 was not effected inthe area of the major cutting edges 8, 9.

On the base layer 26 the aforementioned slide layer 20 is formed whichis indicated by a grey shading in FIG. 3. This slide layer 20 ispreferably prepared on the basis Of sulphide, selenide or telluride andthus has certain lubricating characteristics which will be explained inmore detail in the following. The slide layer 20 does not extend overthe entire cutting maker 2, but ends at a distance from the majorcutting edges 8, 9 so that the latter are formed by the hardwear-resisting base layer 26. I.e., the actual cutting area of the drill1 is covered by the hard base layer 26, which may have, for instance, aVickers pyramid hardness of approx. 2000-10000 HV, while the other areasof the cutting member 2, which do not directly contribute to themachining operation, are covered with the comparatively soft slide layer20 which may have, for instance, a Mohs' hardness of 1-2.

In particular cases, the slide layer 20 may also be applied directly tothe base body so that the same constitutes the base layer.

In order to illustrate the effect of this slide layer 20, FIG. 4 shows asectional view of a cutting edge 28 of a cutting tool during themachining operation. A chip 32 is removed from a workpiece 30 by thefeed motion in the direction of the arrow, the cutting edge 29 beingformed by the hard and wear-resisting base layer 26 in the area wherethe actual machining of the workpiece 30 is performed. The chip isremoved along the face 12 and thus moves on the slide layer 20 indicatedas dashed line which supports the gliding of the chip along the face 12due to its sliding effect (MoS₂ . . . ). In this way, the removal of thechip from the actual machining area is supported so that, on the onehand, the chip and thus also thermal energy can rapidly be dischargedfrom the workpiece and, on the other hand, the face wear is minimizeddue to the special structure, i.e. a hard base layer 26 in the cuttingarea and a soft slide layer 20 in the discharging area of the flutes 4,5, and the formation of a built-up edge is prevented.

Moreover, by producing the slide layer 20 on the open face 10 of thetool, the friction thereof with the machined surface 34 of the workpiece30 is minimized so that also the wear of the open face in the area ofthe cutting edges can be reduced to a minimum. Hence by providing theslide layer 20 the wear of the tool can be substantially reducedcompared to conventional tools having no slide layer 20.

Such tools are thus especially advantageous when used for dry machiningor for the machining with a reduced amount of coolant of light metals(aluminium/magnesium alloys) which becomes increasingly important in theautomotive and aviation industry. When coolants and lubricants aredispensed with or reduced, one the one hand considerable investmentcosts can be saved, on the other hand the recycling or waste disposal ofsuch coolants/lubricants represents a problem which likewise constitutesan increasingly important cost factor in view of strict legislativeimpositions.

The superiority of coated tools to uncoated tools can be explained byway of the comparative tests represented in FIG. 6. These tests werecarried out with a TiAlN-coated twist drill, the tests being executed onthe basis of identical machining parameters (cutting speed, feed,cutting depth). The test series shown on the left of FIG. 6 was carriedout with a workpiece made of AlSi9, wherein an almost tripled tool lifetravel was achieved by the tool provided with a hard base layer and asoft slide layer (H+S).

The same result was obtained also with an Al alloy having a highersilicon content (AlSil8), wherein although on the whole lower valueswere achieved due to the worse machinability of this material, thecoated tool, however, exhibited a considerably longer tool life travelwith otherwise equal test conditions.

I.e. by providing the soft slide layer on a hard base layer or a hardbase body of a tool the tool life and thus also the maximum possiblecutting speeds can be substantially improved compared to conventionaltools. Optimum results can be achieved, when the tool as represented inFIGS. 1 and 3 is provided both with a grooved section and with a softslide layer, wherein it may be advantageous in individual cases toprovide solely either of the described improvements (grqoved section orslide layer).

When forming the grooves 18 and the recesses 14, radii (depths andwidths) ranging from 0.01-2 mm, preferably 0.02-0.5 mm, are preferred.Such grooves 18 and recesses 14 can be produced during grinding theflutes an the drill bit, resp., in one working cycle so that no separategrinding operations and tools are necessary for providing thegrooves/recesses.

The slide layer 20 can be prepared by ion sputtering so that this layeris not only applied to the surface of the base layer 26 but also partlydiffuses into the base layer.

The invention is not restricted to the use with drilling tools, ofcourse, but the grooved section according to the invention and/or theslide layer according to the invention are also applicable to othercutting tools, preferably to those having a geometrically definedcutting face.

What is claimed is:
 1. A cutting tool, comprising: a cutting memberincluding, a base body defining at least one open face and at least oneflute intersecting to form at least one cutting edge configured tosplinter material off a workpiece, said open face and said fluteincluding plural adjacent groove-shaped recesses; forming a continuousundulating cross section at said cutting edge, and a slide layer formedon at least a portion of said base body and having a lower hardness thansaid base body.
 2. A cutting tool according to claim 1, wherein saidslide layer comprises a sulfide, a selenide, a telluride, or a mixedcombination thereof.
 3. A cutting tool according to claim 2, whereinsaid slide layer includes a material selected from the group consistingof MoS₂, NbS₂, TaS₂, WS₂, MoSe2, NbSe₂, TaSe₂, Wse₂, MoTe2, NbTe₂, Wte₂,and mixed compounds thereof.
 4. A cutting tool according to claim 1,wherein said base body of said cutting member comprises a materialselected from the group consisting of high speed steel (HSS), a hardalloy, cermit and ceramic.
 5. A cutting tool according to claim 1,wherein said slide layer is not provided in the area of said cuttingedge.
 6. A cutting tool according to claim 1, wherein a thickness ofsaid slide layer is between 0.01-5 μm.
 7. A cutting tool according toclaim 1, wherein the hardness of said slide layer is between 1-2 on theMohs' hardness scale.
 8. A cutting tool according to claim 1, whereinsaid plurality of adjacent groove shaped recesses of said open faceextend away from said cutting edge toward a rear edge of said open face.9. A cutting tool according to claim 6, wherein said cutting edge isformed on a front edge of said open face and said groove shaped recessesof said open face are arranged in an approximately concentricrelationship relative to a lengthwise axis of said cutting tool.
 10. Acutting tool according to claim 7, wherein said groove shaped recessesof said open face are segments of a circle or spiral.
 11. A cutting toolaccording to claim 1, wherein said groove shaped recesses of said fluteare formed such that an axis of said groove shaped recesses of saidflute run approximately parallel to an axis of said flute.
 12. A cuttingtool according to claim 9, wherein said groove shaped recesses of saidopen face form an approximately undulatory cross section.
 13. A cuttingtool according to claim 9, wherein one of said plurality of grooveshaped recesses of said open face is allocated to one of said pluralityof groove shaped recesses of said flute, respectively, with said onegroove shaped recess of said open face forming an extension of said onegroove shaped recess of said flute.
 14. A cutting tool according toclaim 1, wherein said groove shaped recesses of said open face and saidgroove said recess of said flute extend away from said cutting edge andrun across only a partial section of at-least one of said flute and saidopen face.
 15. A cutting tool according to claim 1, wherein the widthand depth of said groove shaped recesses of at least one of said openface and said flute is 0.01-2 mm.
 16. A cutting tool according to claim1, wherein the width and depth of said groove shaped recesses of atleast one of said open face and said flute is 0.02-0.5 mm.
 17. A cuttingtool, comprising: a cutting member, including a base body defining atleast one open face and at least one flute intersecting at least onecutting edge configured to splinter material off a workpiece, said openface and said flute including plural adjacent groove-shaped recessesforming a continuous undulating cross section at said cutting edge, abase layer formed on at least a portion of said base body, and a slidelayer formed on at least on at least a portion of at least one of saidbase layer and said base body, said slide layer having a lower hardnessthan said base layer and said base body.
 18. A cutting tool according toclaim 17, wherein said slide layer comprises a sulfide, a selenide, atelluride, or a mixed combination thereof.
 19. A cutting tool accordingto claim 18, wherein said slide coating layer includes a materialselected from the group consisting of MoS₂, NbS₂, TaS₂, WS₂, MoSe₂,NbSe₂, TaSe2, Wse₂, MoTe₂, NbTe₂, Wte₂, and mixed compounds thereof. 20.A cutting tool according to claim 17, wherein said base body of saidcutting member comprises a material selected from the group consistingof high speed steel (HSS), a hard alloy, cermit and ceramic.
 21. Acutting tool according to claim 17, wherein said base layer comprises aceramic material.
 22. A cutting tool according to claim 21, wherein saidbase layer includes a material selected from the group consisting ofTiN, TiAlN, TiCN, and diamond.
 23. A cutting tool according to claim 17,wherein said slide layer is not provided in the area of said cuttingedge.
 24. A cutting tool according to claim 17, wherein a thickness ofsaid base layer is between 1-10 μm.
 25. A cutting tool according toclaim 17, wherein a thickness of said slide layer is between 0.01-5 μm.26. A cutting tool according to claim 17, wherein a thickness of saidbase layer is between 1-10 μm and a thickness of said slide layer isbetween 0.01-5 μm.
 27. A cutting tool according to claim 17, wherein thehardness of said base layer is between 1,000 and 10,000 HV and thehardness of said slide layer is between 1-2 on the Mohs' hardness scale.28. A cutting tool according to claim 17, wherein the hardness of saidbase layer is between 2,000 and 4,000 HV and the hardness of saidsliding layer is between 1-2 on the Mohs' hardness scale.
 29. A cuttingtool according to claim 17, wherein a plurality of adjacent grooveshaped recesses of said open face extend away from said cutting edgetoward a rear edge of said open face.
 30. A cutting tool according toclaim 26, wherein said cutting edge is formed on a front edge of saidopen face and said groove shaped recesses of said open face are arrangedin an approximately concentric relationship relative to an axis of saidcutting tool.
 31. A cutting tool according to claim 27, wherein saidgroove shaped recesses of said open face are segments of a circle orspiral.
 32. A cutting tool according to claim 17, wherein said grooveshaped recesses of said flute are formed such that an axis of saidgroove shaped recesses run approximately parallel to an axis of saidflute.
 33. A cutting tool according to claim 30, wherein said grooveshaped recesses of at least one of said open face and said flute form anapproximately undulatory cross section.
 34. A cutting tool according toclaim 30, wherein one of said plurality of groove shaped recesses ofsaid open face is allocated to one of said plurality of groove shapedrecesses of said flute, respectively, with said one groove shaped recessof said open face forming an extension of said one groove shaped recessof said flute.
 35. A cutting tool according to claim 17, wherein saidgroove shaped recesses of said open face and said groove shaped recessof said flute extend away from said cutting edge and run across only apartial section of at least one of said open face and said flute.
 36. Acutting tool according to claim 17, wherein the width and depth of saidgroove shaped recesses of at least one of said open face and said fluteis 0.01-2 mm.
 37. A cutting tool according to claim 17, wherein thewidth and depth of said groove shaped recesses of at least one of saidopen face and said flute is 0.02-0.5 mm.